Halogen-free systems

Base polymer Filler lII.94/glow wire test (°C) CTl (comparative tracking index) Example Notes 

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This table illustrates pretty well that the large-scale ionic liquid will probably not comprise a diallcylimidazolium cation and a [CE3S02)2N] anion. Over a medium-term timescale, we would expect a range of ionic liquids to become commercially available for 25-50 per liter on a ton scale. Halogen-free systems made from cheap anion sources are expected to meet this target first. 

The author anticipates that the further development of transition metal catalysis in ionic liquids will, to a significant extent, be driven by the availability of new ionic liquids with different anion systems. In particular, cheap, halogen-free systems combining weak coordination to electrophilic metal centers and low viscosity with high stability to hydrolysis are highly desirable. 

If there are at least two atoms of chlorine per titanium atom in the system, then, besides a 1 1 titanium-aluminum complex, a 1 2 complex also exists, as shown by NMR spectroscopy (160). Because, even at low temperatures, a coalescence of the alkyl groups on the aluminum cannot be found, a simple Ti—Cl — Al donor bond could be present. In agreement with this idea, no complex formation occurs with the halogen-free system (C5H5)2TiMe2-AlMe3. After formation of the complex, alkylation of the titanium component is presumed to take place. 

BASF is the only producer of propionic acid by the carbonylation of ethylene, which is reacted exothermically AH - -64.5 kJ/mol) with carbon monoxide and water. Nickel chloride was patented as early as 1943 as a catalyst for the carbonylation of ethylene [8], For the industrial-scale process, however, a halogen-free system is used [9, 10]. Propionic acid is formed according to eq. (2). 

Less than 10% of the polyamide produced is made in a flame retardant version. The best system is composed of a combination of red phosphorus and zinc borate (see table above). The only drawback of this system is its color which is restricted to brick red or black. If other colors are required, ammonium polyphosphate is used either in combination with organic flame retardants or with antimony trioxide. It is possible to manufacture a very wide range of colors in the halogen free system. Some systems make use of the addition of novolac or melamine resins. For intumescent applications, ammonium polyphosphate, in combination with other components, is the most frequently used additive. Figure 13.6 shows that fillers such as calcium carbonate and talc (at certain range of concentrations) improve the effectiveness of ammonium polyphosphate. This is both unusual and important. It is unusual because, in most polymers, the addition of fillers has an opposite influence on the efficiency of ammonium polyphosphate and it is important because ammonium polyphosphate must be used in large concentrations (minimum 20%, typical 30%) in order to perform as a flame retardant. 

Flame Retardants Processors learn to ivork ivith halogen-free systems. Modem Plastics International, 23,9, pp. 39-41 (1993). 

Halogenated systems in the gas phase act by interrupting the radical chain mechanism that sustains the flame, whereby they are highly efficient. The different halogen-free systems, on the other hand, work like this ... 

The most important representative of the antimony flame-retardants is antimony trioxide (Sb203 or Sb406). It has very little if any effect on non-halogenic polymers or in halogen-free systems. In the presence of halogens, however, a very strong synergetic effect multiplies the fiame-retardancy. 

No fundamentally new fire retardant (FR) systems have been developed in recent years. However, many improvements have been made to existing ones as a drive to halogen-free systems has stirred R D teams. Such developments can prove very difficult in many cases on technical and cost groimds. 

This is borne out by new developments such as nanocomposites in the cable field and in nanotechnology for PC/ABS blends. Over the medium term, all plastics will be available with halogen-free systems. It will then be possible to cover all the different requirements with the established and the new FR plastics and thus serve the market in an optimum fashion. 

Joseph Storey has introduced a zinc hydroxystannate flame retardant, which it found to be the closest non-toxic alternative to antimony trioxide in halogenated systems. The new material also has excellent smoke suppression properties. In halogen-free systems, tin char formation occurs, leading to reductions in filler loadings and improved physical properties. 

Further possible additives include aliuniniiun hydroxide, magnesium hydroxide and magnesium carbonate. Intumescent systems are increasingly promoted when a halogen free system is requested. 

As with other sectors, an increasing number of OEMs in the electrical world will insist on halogen-free systems for their products. This extends to the printed circuit boards (PCBs) used to make them. Even the phosphoms systems mentioned above are likely to come under scmtiny as well. 

Zinc borate can be used as a fire retardant in PVC, polyolefins, elastomers, polyamides, and epoxy resins. In hal( en-containing systems, it is used in conjunction with antimony oxide, while in halogen-free systems it is normally used in conjunction with other FRs such as aluminum trihydrate, magnesium hydroxide, or red phosphorus. In a small number of specific applications, zinc borate can be used alone. 

APP and APP-based systems are very effident halogen-free flame retardants mainly used in polyolefins (PE, PP), epoxies, polyurethanes, unsaturated polyesters, phenolic resins, and others. APP is a nontoxic, environment friendly material and it does not generate additional quantities of smoke due to intumescence. Compared to other halogen-free systems, APP requires lower loadings. In thermoplastic formulations, APP exhibits good processability, retention of good mechanical properties. 

With halogen-containing systems, zinc borate can partially or completely replace the antimony synergist in PVC, notably wire and cable, wallcoverings, roof membranes and tarpaulins. It is also effective in polyolefins, elastomers, polyamides and epoxy polymers while, in halogen-free systems, it can be used in conjunction with alumina trihydrate, magnesium hydroxide or red phosphorus. 

Materials/characteristic.s Some inorganic fillers. Nitrogen-donors melamine compounds. Antimony compounds with halogen donors. Halogenated containing chlorine, bromine. Halogen-free systems aluminium trihydroxide (ATH), magnesium hydroxide, zinc borate. Intumescent systems phosphorus compounds. 

A key driver of change and new product development in the plastics additives markets is a host of environmental concerns. This is seen most dramatically in PVC where concerns over the use of heavy-metal heat stabilizers based on lead have led to a widespread conversion to tin-based materials and even to nonmetallic stabilizers. The widely used phthalate-based Plasticizers for flexible PVC have come under fire because of concerns over their potential adverse effects on the human reproductive systems. Concerns over the potential for brominated FRs to form dioxins are fueling the development of new halogen-free systems. 

Special considerations copper compounds catalyze thermal and UV degradation titanium dioxide lowers UV stability, titanium dioxide is used as agent red phosphorus in combination with zinc borate gives V-0 or V-1 rating with halogen-free system and inhibits corrosion because it can trap trace amounts of phosphine produced from red phosphoms... 

K. Shen and E. Olsen, eds.. Recent Advances on the Use of Borates as Fire Retardants in Halogen-Free Systems Proceedings of the 16th Annual BCC Conference on Flame Retardancy (Stamford, CT BCC Research, 2005). 

Flame retardants halogen free systems (including phosphorus... 

There are three essential conditions to be met if a polymer, once ignited, is to continue burning. There must be a supply of heat to the bulk polymer, a generation of fuel (typically volatile decomposition products) and there must be a flame. Halogen-based systems act by a well-documented flame poisoning mechanism in the vapour phase. The alternative halogen-free systems, which encompass a wide variety of additives, tend to act by mechanisms which disrupt heat flow and the supply of fuel to the flame. Here the mechanisms are not always understood in great detail but two broad types of flame retardant action can be defined. 

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